1. Field of the Invention
This invention relates to a liquid crystal display device and an electronic device including the display device, specifically to a liquid crystal display device using an active matrix substrate.
2. Description of the Related Art
A liquid crystal display device with an active matrix circuit using active devices such as TFTs (Thin Film Transistors) has come into widespread use including a laptop PC and a monitor in recent years.
In a liquid crystal display device using a conventional nematic liquid crystal material, a display status of each pixel is controlled by an electric potential difference between a pixel electrode switched by the active device and a common electrode. When a large electric potential difference is applied between the pixel electrode and the common electrode, that is, when black is displayed in a normally white mode or when white is displayed in a normally black mode, a maximum electric potential difference between the common electrode and the pixel electrode is usually three to five volts, although it varies depending on the liquid crystal material used, a mode of the liquid crystal and a gap of the liquid crystal. In order to secure reliability of the liquid crystal device, the liquid crystal display device requires inverting a polarity of voltage applied to the liquid crystal at a certain interval, or an alternating current drive. Assuming that the electric potential of the common electrode is fixed, the electric potential amplitude of a signal written into the pixel electrode, that is, a video signal inputted to a data line of the active matrix circuit, is six to ten volts.
When the video signal inputted to the data line is written-in by an external data driver IC, however, an expensive IC manufactured, not only by a conventional CMOS process but by a high withstand voltage process, is required in order to output the electric potential amplitude higher that five volts, leading to an increased cost and increase power consumption. To solve the problem described above, a drive method to reduce by half the amplitude of the input signal to the data line by using a common inversion drive in which the polarity of the common electrode is alternated is proposed in Japanese Patent Application Publication No. S62-49399, for example.
When the common inversion drive proposed above is applied to a large and high resolution display panel, however, capacitance of the common electrode is increased to increase a relaxation time and the maximum instantaneous current at a common electric potential inversion timing.
This invention is directed to solving the problems addressed above, and offers a liquid crystal display device and an electronic having the display device, which are small in dimensions of periphery of the panel and low in power consumption.